thunderbolt: dma_test: Use correct value for absent rings when creating paths

Both tb_xdomain_enable_paths() and tb_xdomain_disable_paths() expect -1,
not 0, if the corresponding ring is not needed. For this reason change
the driver to use correct value for the rings that are not needed.

Fixes: 180b0689

 ("thunderbolt: Allow multiple DMA tunnels over a single XDomain connection")
Cc: stable@vger.kernel.org
Reported-by: Pengfei Xu <pengfei.xu@intel.com>
Tested-by: Pengfei Xu <pengfei.xu@intel.com>
Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>